A scanning visitor of program elements with default behavior
appropriate for the RELEASE_7
source version. The visitXYZ methods in this
class scan their component elements by calling scan on
their enclosed elements,
parameters, etc., as
indicated in the individual method specifications. A subclass can
control the order elements are visited by overriding the
visitXYZ methods. Note that clients of a scanner
may get the desired behavior be invoking v.scan(e, p) rather
than v.visit(e, p) on the root objects of interest.

When a subclass overrides a visitXYZ method, the
new method can cause the enclosed elements to be scanned in the
default way by calling super.visitXYZ. In this
fashion, the concrete visitor can control the ordering of traversal
over the component elements with respect to the additional
processing; for example, consistently calling
super.visitXYZ at the start of the overridden
methods will yield a preorder traversal, etc. If the component
elements should be traversed in some other order, instead of
calling super.visitXYZ, an overriding visit method
should call scan with the elements in the desired order.

Methods in this class may be overridden subject to their
general contract. Note that annotating methods in concrete
subclasses with @Override will help
ensure that methods are overridden as intended.

WARNING: The ElementVisitor interface
implemented by this class may have methods added to it in the
future to accommodate new, currently unknown, language structures
added to future versions of the Java™ programming language.
Therefore, methods whose names begin with "visit" may be
added to this class in the future; to avoid incompatibilities,
classes which extend this class should not declare any instance
methods with names beginning with "visit".

When such a new visit method is added, the default
implementation in this class will be to call the visitUnknown method. A new element scanner visitor
class will also be introduced to correspond to the new language
level; this visitor will have different default behavior for the
visit method in question. When the new visitor is introduced, all
or portions of this visitor may be deprecated.